When the US declared war on Germany on April 6, 1917, the Allies had already endured over three years of carnage.

The famed Harlem Hellfighters were the first to join the fight on the frontlines under French command.

As the Americans began to send more troops across the Atlantic, Germany was anxious to score a victory before the majority of their forces arrived.

In the midst of the Bolshevik Revolution, Russia could not sustain its war effort. The dissolution of its forces freed German soldiers to the east, and the Central Powers' ranks along the western front swelled.

The plan for Kaiserschlacht, or "Kaiser's battle," was to conquer Paris, and end the war.

That plan backfired, and with the additional US troops, the Allies were able to counter a string of German offensives, starting with the first US-led assault in a small village near the Somme called Cantigny.

Americans captured 100 German soldiers during their first offensive at Cantigny.

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American troops from 28th Infantry Regiment of First Division, American Expeditionary Forces go 'over the top' on May 28, 1918.

(Associated Press)

Launched May 28, 1918, the Battle of Cantigny was America's first major offensive in World War I.

Americans show their strength at Cantigny, and prove their forces can stand alone.

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American troops take defensive positions in a wrecked building in Cantigny, France in 1918.

(Hulton Archive/Getty)

American forces seized the village of Cantigny in just over half an hour, and defended against several German counterattacks for the next two days.

Under Army general John Pershing's orders not to surrender an inch, Americans held their positions at the cost of over 1,000 lives.

'Come on, you sons of bitches, do you want to live forever?'

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Exhausted and depleted, members of the 6th Marine regiment gather after the fighting ended outside of Belleau Wood.

(US Marine Corps/Wikimedia Commons/Public Domain)

German reinforcements, recently arrived after their relocation from the eastern front, continued their offensive at Chateau-Thierry, and advanced within 50 miles of Paris before pausing in Belleau Woods.

It was there the Americans decided to attack. As they dug in to prepare for the days ahead, their French counterparts retreated, and advised the US Marines do the same.

On June 6, 2018, the US forces launched a three-week battle in which both sides would suffer debilitating losses.

On the first day of fighting, US forces suffered over 1,000 casualties. The Germans defended against nine assaults, until June 26, when a combat report relayed the victory.

Accounts vary as to the precise wording used by Marine Maj. Maurice Shearer, but the gist was this: "Woods now U.S. Marine Corps entirely."

'US Marines smash Huns' and build a legacy.

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Bodies of German soldiers who were killed at Belleau Wood, 1918.

(Associated Press)

War correspondent Floyd Gibbons' headline for the Chicago Tribune, and the battle in which he lost an eye, would form a legacy the US Marines treasure to this day.

Throughout the battle, Americans suffered nearly 10,000 casualties.

Germany's final offensive goes awry in the Second Battle of the Marne.

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Second Battle of the Marne, 1918.

(Hulton Archive/Getty)

Germany launched its final offensive on July 15, 1918.

Suffering a major defeat at Belleau Wood, German General Erich Ludendorff had one final chance to advance across the river Marne towards Paris.

But the Allies held him off, and on July 18 launched a counter-offensive that would be considered the turning point of the war.

With a German retreat, the Allies advance to victory.

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This photo from the Battle of the Marne shows tanks and aircraft, two major developments in warfare during The Great War.

(Hulton Archive/Getty)

The Franco-American troops, with an estimated 300 tanks, forced the Germans to retreat.

Gen. Ludendorff's plan was to divert the Allies away from Flanders, where he would launch another offensive.

But the Germans suffered a swift defeat, and by early August 1918 the Allies had recaptured Soisson to the north.

Germany was now on the defensive.

Colonel Patton's troops draw first blood at St. Mihiel.

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A group of captured Germans at St. Mihiel Salient in 1918.

(Hulton Archive/Getty)

A headline from The New York Times read:

"Americans wipe out St. Mihiel Salient, taking nearly 13,300 prisoners and many guns."

After a swift victory, American forces prepared to break the Hindenburg Line.

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American troops on the front lines of St. Mihiel cheer after hearing an Armistice has been signed in November 1918, bringing an end to World War I.

(Associated Press)

The German evacuation at St. Mihiel had reportedly already begun.

The swift victory allowed US forces to transfer to the Meuse-Argonne to support the Allies' next major offensive.

The Allies' final push at the Meuse-Argonne.

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A US Army 37mm gun crew man their weapons on September 26, 1918 during the Meuse-Argonne Allied offensive.

(Associated Press)

In October 1918, US President Wilson rejected a request for armistice by German Chancellor Prince Maximillian.

Meanwhile, the American Expeditionary Forces drove the Germans into retreat in a final offensive at the Meuse-Argonne.

After a decisive Allied victory, Germans accept defeat and sign for peace.

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A commanding officer and his staff from the 58th Infantry Regiment use a concrete slab as a makeshift operations table to discuss the next step in the Meuse-Argonne advance, 1918.

(General Photographic Agency/Getty)

Over 1 million Americans fought in the battle, a decisive Allied victory that brought an end to The Great War.